Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $53.40   11.352%   $59.462   $59.46   $59.45   $59.50  
  Purchase #2 $250.69   3.851%   $260.3441   $260.34   $260.35   $260.30  
  Purchase #3 $228.66   4.516%   $238.9863   $238.99   $239.00   $239.00  
  Purchase #4 $33.82   8.593%   $36.7262   $36.73   $36.75   $36.70  
  Purchase #5 $175.30   10.486%   $193.682   $193.68   $193.70   $193.70  
  Purchase #6 $123.40   4.370%   $128.7926   $128.79   $128.80   $128.80  
  Purchase #7 $208.70   10.681%   $230.9912   $230.99   $231.00   $231.00  
  7 purchase totals = $1,073.97       $1,148.9844   $1,148.98   $1,149.05   $1,149.00